The present invention generally relates to a system for encoding and decoding an analog signal. More particularly, the present invention pertains to a system including an encoder for encoding an analog signal as a series of pulses, and a decoder for receiving and decoding the series of transmitted pulses so as to output an analog signal corresponding to the analog signal received by the encoder.
Systems and methods are known that include an encoder for encoding an analog signal as a digital signal for purposes of enhancing transmission. Such systems include a decoder circuit that receives the transmitted digital signal and converts it back into an analog signal resembling the analog signal received by the encoder. By encoding the analog signal into a digital signal prior to transmission, the transmitted signal will be less likely to be adversely affected by noise that is present in the environment through which the signal is transmitted. One type of system used for this purpose employs linear pulse code modulation (PCM) in which the quantizing step sizes are constant. Such systems, however, require a relatively broad transmission bandwidth to have sufficient resolution. Further, PCM systems typically employ high precision components that are relatively expensive.
Other systems used to encode and decode analog signals are delta modulation systems. Although delta modulation systems are typically less expensive, they generally require much higher bit rates than PCM systems if it is desired to achieve the same quality transmission. Another variation is the adaptive delta modulation (ADM) system. ADM systems are also relatively complex and expensive while requiring a fairly broad transmission bandwidth.
Other systems employ rate coding whereby the amplitude of the analog signal is encoded by a plurality of pulses of equal magnitude such that the frequency of the series of pulses are representative of the amplitude of the analog signal. In such a system, the decoder determines the frequency of the received pulses by counting the number of pulses detected within a predetermined time window. Thus, such a rate coding system requires the transmission of a plurality of pulses at a particular frequency in order to inform the decoder of each incremental change in amplitude level. Accordingly, for a rapidly varying analog signal, the system must be capable of transmitting pulses at a very high frequency as well as receiving and decoding these pulses at a very high rate. Therefore, to obtain the responsiveness typically needed for these types of systems, the encoder and decoder are typically relatively complex and expensive.